1. Field of the Invention
The present invention relates generally to an apparatus for swiveling an injection unit of a motor-driven injection molding machine. More specifically, the invention relates to an apparatus for smoothly and automatically swiveling an injection unit by utilizing the drive power of a nozzle touch mechanism for producing a turn on a pivot pin.
2. Description of the Prior Art
In an injection unit of an injection molding machine, it is required to detach a screw from a heating cylinder for maintenance of the screw, the heating cylinder and so forth. In order to facilitate the maintenance work, it is required to swivel the injection unit to prevent it from interferes with a fixed die plate, after moving the injection unit backward from a nozzle touch position.
Since the injection unit is too heavy to be manually handled, a dedicated device for swiveling the injection unit is provided to accomplish the automatic swiveling motion. In conventional hydraulic injection molding machines, a swiveling device and a nozzle touch mechanism use the same hydraulic cylinder both for carrying out the nozzle touch motion and the swiveling motion.
In recent years, with the advantages of easy control and energy saving effect, motor-driven injection molding machines come into wide use in place of hydraulic injection molding machines. For motor-driven injection molding machines, various swiveling devices have been known. A typical swiveling device for a motor-driven injection molding machine is disclosed in Japanese Patent Publication No. 1992-27933. As shown in FIG. 11, an injection unit base 5, in which an injection unit is installed, is pivotable with respect to an extruder base 6 by means of a pivot pin 7. The extruder base 6 has a elongated hole 16. The elongated hole 16 extends from the center line, at which the pivot pin 7 is provided, to a side, and extends so as to go away from a front edge 6a. A drive pin 8 passes through the elongated hole 16 to be fixed to a ball nut 10. This ball nut 10 engages with a ball screw 11 included in a nozzle touch mechanism. This swiveling device can utilize the nozzle touch mechanism to accomplish a swiveling function while moving the extruder base 6 and the injection unit base 5 backward.
In the past, most of motor-driven injection molding machines had been belonged to small class of machines. In recent years, motor-driven injection molding machines in medium or large class have been developed and widely spread. In such a motor-driven injection molding machine in medium or large class, the injection unit is so heavy that the load applied on the ball screw and ball nut of the nozzle touch mechanism unavoidablly increases.
In addition, as shown in FIG. 11, when the nozzle touch mechanism is utilized for swiveling the injection unit while backward movement, a bending load synthesized by a radial load and a moment load is applied on the ball screw 11 of the nozzle touch mechanism, so that the uniformity of the load applied on the ball screw 11 is damaged to remarkably reduce its service life. For that reason, the diameter of the ball screw is inevitably increased than a diameter of the ball screw that meets requirement for the nozzle touch force. Therefore, the space for installing the nozzle touch mechanism is increased in order to build the large-diameter ball screw 11 and the ball nut 10 therein.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a swiveling device at a space saving capable of smoothly swiveling an injection unit of a electric motor-driven injection molding machine by using a function of the nozzle touch mechanism without applying an excessive bending load on a ball screw, even if the motor-driven injection molding machine belongs to a medium or large class of the machine.
In order to accomplish the aforementioned and other objects, according to one aspect o the present invention, there is provided an apparatus for swiveling an injection unit of a motor-driven injection molding machine, said apparatus comprising: a slide base provided on a frame so as to be linearly movable; an injection unit base for mounting an injection unit thereon, pivotably stacked on the slide base; a nozzle touch mechanism having a motor and a screw feed mechanism for converting the rotation of the motor into thrust force and transmitting the thrust force to the slide base to connect and disconnect a nozzle of the injection unit with a mold; a pivot member connection the slide base with the injection unit base for forming the center on which the slide base is turned around; and a swiveling means for converting forward movement of the injection unit base into swiveling movement by restraining the injection unit base from advancing so that the slide base driven by the screw feed mechanism is allowed to advance.
The swiveling means may comprises a pin connecting means arranged between the injection unit base and the frame at a position deviated from the pivot, the pin connecting means integrated with the injection unit base; a pivot connecting pin member capable of connecting and disconnecting with the pin connecting means; a pin supporting means, secured to the frame, for supporting said pivot connecting pin member so as to is connectable with the pin connecting means; and a pin operating means for causing the pivot connecting pin to engage with or disengage from the pin connecting member.
The pin connecting portion may comprise an arm portion, which protrudes from one side portion of the injection unit base, and a long groove which is formed in the arm portion and which receives the pivot pin therein.
Alternatively, the pin connecting portion may comprise an arm portion, which protrudes from one side portion of the injection unit base, and a link member, one end of which is connected to the arm portion via a pin, and the other end of which is connected to the pin supporting portion by the pivot pin.
The injection unit base may comprise a front base and a rear base, and the pivot pin is mounted on any one of the front base or the rear base.
According to the present invention, by inserting the pivot pin into the pin connecting portion, the forward movement of the injection unit base is restricted by the pivot pin, and the slide base continues to move forward. Therefore, if the injection unit base intends to move forward with the slide base, the pin connecting portion gradually swivels the injection unit base about the pivot. Since the slide base connected to the ball screw feed mechanism of the nozzle touch mechanism moves only forward and rearward, no excessive loads, such as a bending load, are not applied on the ball screw.